1. Field of the Invention
The present invention relates to a headrest apparatus for a vehicle, such as an automobile.
2. Description of Related Art
Japanese Patent Application Laid-open No. 7-291005 discloses an automotive seat-back structure for a passenger""s head when the passenger""s vehicle has a rear-end collision.
According to this seat-back structure, at the vehicle rear-end collision, a dynamic load of inertia exerted on the passenger is born by a seat-back and then, a component member of the seat-back moves. Then, this movement of the member is transmitted to a headrest support arm, so that a headrest body moves forward. In this way, the above seat-back structure is capable of preventing the passenger""s head from being moved back excessively.
Japanese Utility Model Application Laid-open No. 6-59163 discloses an air bag apparatus which can prevent the passenger""s head from being moved back even if a space is remained between the passenger""s neck and the headrest body at the vehicle rear-end collision. This airbag apparatus includes a sensor that is activated by inertia force of the passenger at the vehicle rear-end collision and an air bag accommodated in the head rest body and also inflated by the so-activated sensor.
In the firstly-mentioned seat-back structure, however, when the backward displacement of the passenger gets larger (more than a predetermined value), it is started to move the head rest body forward. Therefore, under a situation that the displacement of the passenger is relatively small immediately after the collision, there arises a problem of impossibility to move the head rest body sufficiently forward.
In the secondary-mentioned air bag apparatus, since an explosion sound is generated when expanding the air bag, there is a possibility of increasing a burden on a passenger""s ear.
Under the above circumstance, it is an object of the present invention to provide a headrest apparatus for a vehicle, which thrusts the headrest body forward about the vehicle on detection of the vehicle rear-end collision, whereby the passenger""s head can be held certainly and rapidly without making use of the passenger""s inertia at the vehicle rear-end collision.
According to the present invention, the above-mentioned object is accomplished by a headrest apparatus for a vehicle, comprising a headrest body attached to an upper end of a seat-back through stays to support a passenger""s head; wherein the headrest body includes a pair of left and right headrest members separated from each other at a substantial center of the headrest body in the left-and-right direction of the vehicle, the left and right headrest members each having one separation end adjacent to the other headrest member and the other end in opposition to the separation end, rotatably attached to the stay; a sheet stretched between the separation ends of the left and right headrest members; rotating-and-urging mechanisms for rotating and urging the left and right headrest members forward about the vehicle, respectively; a locking unit for holding the left and right headrest members at their initial positions in opposition to urging forces by the rotating-and-urging mechanisms; and a control unit for releasing the locking unit on detection of a rear-end collision of the vehicle.